The invention concerns a tensioning handle for a root-canalling instrument in accordance with the preamble of the base claim.
A tensioning handle of this type is known from German Patent 3 403 654 (U.S. Pat. No. 4,582,489). It has a grip with an outside-threaded shank at one end. An inside-threaded cap screws onto the shank. A bore extends axially through the grip, shank, and cap. Between the shank and the cap is a tensioner. A tool is inserted into the bore, and the threaded components are screwed tight, forcing the tensioner against the shaft of the tool. The tensioner is a conventional helical spring that loosely surrounds the tool shaft opposite the threads, with its ends accommodated in depressions in the threaded components. When the cap is screwed onto the shank of the grip, the spring is entrained at its ends and rotated in. Its coils wrap tight around the tool shaft and secure it. The spring must be manufactured and its ends inserted into the depressions that accommodate them with particular care to ensure reliable tension and easy employment of the cap. A handle of this type is accordingly expensive. Another tensioning handle of a similar design is known from German Patent 2 703 637. It employs a tensioner in the form of a washer instead of a spring. A bore that accommodates the shaft of the tool extends at an angle through the disk but in alignment with the bore through the threaded components. When the threaded components are screwed together, the disk is shifted out of its rest position, with its bore at an angle to that through the threaded components, and compressed. Here again, the manufacturing process is expensive because even slight deviations in the tolerance of such a small component can impair is effectiveness.